on our broadcast tonight, opening night for the democrats here in charlotte. and tonight the first lady is the star attraction of this convention as it gets underway tonight. our political team is here in place. now what? the video that shows the new tsa inspection method at the airport. this time in the waiting area at the gate. testing the liquids people can only buy inside the airport. is it worth it? the new data out on organic food, and why a lot of people may be wondering if their money might not be better spent. and making space. the plan to cut down hundreds of big beautiful trees on the streets of l.a. so the space shuttle can travel by road. "nightly news" from charlotte begins right now. captions paid for by nbc-universal television

good evening. and if it's tuesday, it must be charlotte. the second of the two conventions this political season. and the democrats, the incumbents get to bat last. a lot has changed since the last time they gathered during those days of hope and change. the nation remains mired in an economic downturn. back then, americans were serving in uniform on two fronts overseas. and as of tonight, the nation is still at war. president obama, the incumbent, now has an opponent to run against. this is the chance for obama/biden to make their case against romney/ryan. to ask americans for their vote again. tonight we'll see the keynote, and then hear from first lady michelle obama. and with that ahead of us, let's go to our political team here in charlotte. four white house correspondents, current and former, beginning with our chief white house correspondent, chuck todd down

on the floor of the north carolina delegation. chuck, good evening. >> reporter: good evening, brian. if the republican convention was all about trying to present mitt romney's softer side, the democratic convention has a different goal for the president. shoring up key parts of his voting coalition. tonight the target, hispanics and women. as workers inside the hall put finishing touches on the convention stage, democrats prepare to appeal to two key constituencies, women and hispanics, that favor the president but lack the enthusiasm they had for him four years ago. leading the charge on women, michelle obama. >> are you ready for this? >> reporter: in all, five of the prime time speakers tonight at the convention are women. charged with delivering tonight's official keynote address, julian castro, the 37-year-old mayor of san antonio. democrats hope his personal story will resonate with latinos. >> my mother worked very hard so that joaquin and i could have a very good shot in life and reach

our dreams. >> reporter: joaquin is castro's twin brother, who will introduce him tonight. castro is one of six hispanics speaking tonight. but while modern conventions are tightly scripted affairs, before this gathering even started, a basic question tripped up the democrats. >> can you honestly say that people are better off today than they were four years ago? >> no, but that's not the question of this election. >> reporter: while martin o'malley reversed himself the next day. >> we are clearly better off as a country because we're creating jobs rather than losing them. >> reporter: it hasn't stopped the republican ticket from exploiting the misstep. even adding an are you better off sign to paul ryan's podium. >> he cannot tell you that you're better off. after getting -- after four years of getting the runaround, what america needs is a turnaround. and the man for that job is mitt romney. >> reporter: and now republicans are making hay over this answer the president gave to a colorado tv station about his handling of the economy. >> you've had three and a half years to fix it, what grade

would you give yourself so far for doing that? >> you know, i would say incomplete. but what i would say is the steps that we've taken in saving the auto industry, and in making sure that college is more affordable in investing in clean energy and science and technology and research, those are all the things we're going to need to grow over the long term. >> reporter: a little irony on the are you better off argument, brian, jimmy carter, the man ronald reagan defeated using that very question, he addresses the convention tonight by videotape. also of note, there will be a tribute to the last person to defeat mitt romney in a general election, the late ted kennedy. brian? >> chuck todd starting us off from the floor. which brings us to andrea mitchell who will have one of the best seats in the house, just off the podium here, with a preview of the first lady's appearancen to the, andrea? >> reporter: good evening, brian. michelle obama is a political superstar, much more popular

than her husband. once a reluctant campaigner, now she's a woman with a mission. michelle obama is now a political pro and her husband's best campaigner. hardly needing to practice with the teleprompters or getting a feel for the stage. aids say she will try to project empathy toward struggling middle class families and motivate women voters. >> this election ladies is a choice about supporting women and families in this country. >> reporter: the president said he'll be watching at the white house. >> i'm going to be at home and watching it with our girls, and i am going to try not to let them see their daddy cry. because when michelle starts talking, i start getting all misty. >> reporter: ryan seacrest asked mrs. obama about ann romney's speech. >> ann romney wants to be the new first lady, she gave a much buzzed about speech at the rnc. what was your reaction to her speech? >> you know, i didn't watch it. >> reporter: in her speech, mrs.

obama will try to inspire young people to vote. here with ross matthews for e! news. >> voting is how this country runs. and it's our responsibility, at whatever age, to exercise the rights that people before us fought so hard for us to have. >> reporter: in the white house, she's worked for military families, fought childhood obesity, become a regular on late night. >> being out there, touching people, talking to people, it really gets me focused on what we're doing and why we're doing it. >> reporter: and if her husband is sometimes called too cool, she's all about hugs, connecting to people with a physical embrace. >> look, she's completely at ease, completely comfortable. again, the best advocate that we could possibly have for the president. >> reporter: four years ago, mrs. obama was trying to make america more comfortable with her. now she's trying to make americans feel better about her husband. brian? >> andrea mitchell down near the podium for us tonight. andrea, thanks. by the way, if it sounds a little louder here at the convention, there's no glass

behind us as there was in tampa, so we're wearing these. i plomsed more white house correspondents, i have two more here in the booth. former white house correspondent savannah guthrie and david gregory. they've both moved on to other day jobs since. let's talk about the first lady and the role this puts her in. >> this was someone who was kind of thrust into public life and not enthused about this public role. i talked to an aide today, who said, she's comfortable with the fact that her kids are okay. they're being raised up in as normal a situation as they can be. that's allowed her to expand her horizons. you used to hear white house aids grumble she didn't get out on the campaign trail as much as they'd like. i had one tell me today, she gave us more dates on the campaign trail than we expected or hoped for. and they also say, it goes without saying, she appeals to women, certainly, minority voters. there's no audience they

wouldn't be comfortable putting her in front of right now. >> david, let's talk about the keynote, there are some who predict they will take texas and turn it purple and eventually blue in the next couple of years. >> they want to highlight the young mayor julian castro. you think about nevada or colorado, even this state, there's a feeling among the democrats that republicans made some in roads with their show of diversity. they want to lead with their best foot, remind hispanics that the democratic place is the home for them. critical to the president's re-election chances that he runs up that number with hispanic voters. >> david gregory, savannah guthrie, thanks to you both. a quick note tomorrow here in charlotte, we're going to sit down for an exclusive interview with former president clinton. that's hours before he is due to address this gathering. we'll have that interview for you here on "nightly news" tomorrow night.

brief update on our weather. while it's hard to separate what are the remnants of hurricane isaac from just plain late summer rain, it was a lot of each today that rained out the u.s. open in new york. it's also a big factor this week here in charlotte. a big predicted chance of precipitation every day this week, including thursday when the president's speech is supposed to be in an outdoor open stadium. the democrats say they'll go ahead with it, unless, of course, it becomes a public safety issue. as you see, there's a lot of rain out there. and there is a new tropical storm, leslie, 600 miles south of bermuda. not moving much, but kicking up the surf in places like puerto rico. we mentioned this at the top of the newscast, the tsa is in the news again tonight. and some travelers may decide they have reached their limits when they hear about this one. for all we've had to get used to over the last few years, shoes off, belts off, laptops out, no liquids allowed, there's

something new. would you believe testing the liquids you yourself buy inside the terminal where we're allowed to have liquids? our report from nbc's tom costello. >> reporter: an unexpected sight at the columbus airport, two tsa officers holding a test strip over passenger's drinks to check for explosive vapors, after the passengers had already cleared security and bought the beverage in the concourse. dan holland was there with his wife and son. >> having someone come up to me and demand that i submit to another search without really any probable cause seems a bit much. >> reporter: the tsa says the drink screening has been going on for years as it employs multiple layers of security throughout the airport. it limited passenger's carry on liquids and gels in 2006. after terrorists plotted to blow up u.s. bound passenger planes with u.s. explosives over the atlantic. screening drinks bought in the gate area is meant to guard against potential threats from

inside the concourse, perhaps an employee who could smuggle in an explosive and hand it off to a passenger. but while airline passengers face the prospects of additional screening every day, neither the trusted vendors nor the airport employees are screened every day. and the tsa won't say how often they are screened. screening drinks bought in a supposedly secure environment garnered mixed reaction in chicago today. >> kind of ridiculous, excessive maybe. >> i would rather get on a plane knowing i'm safe. >> i think it's a worthwhile thing for them to do. you can't be too safe. >> i am a little concerned about how invasive its getting. >> reporter: passengers who decline the beverage check may be denied boarding. two years ago the tsa invited us into its laboratories as it tested equipment it hoped could sniff out explosives inside plastic bottles. >> we're trying to measure and quantitate how much of a gas is leaking out from a liquid via plastic seals and bottles. >> reporter: but foolproof

technology has proven illusive. an unpredictable offense at airports remains the best defense. tom costello, nbc news, washington. and still ahead as we continue tonight, is eating organic food actually better? it sure does cost more. tonight we'll show you what a team of doctors concluded when they looked through all the available evidence. and later after the great success of the summer olympics, we'll show you the new games in town.

we're back now with health news getting a lot of attention. it's about organic foods. people who buy them and pay more for them do it for a lot of reasons, mostly because they think they're healthier. but are they? our report tonight from our chief medical editor dr. nancy snyderman. >> reporter: in supermarkets across the country and at farmers markets from coast to coast, increasingly, americans are buying organic. in 1997, u.s. seals of organic

foods topped off at $3.6 billion. fast forward to 2010, sales total more than $26 billion. the reason? >> you want to put something on your table that's healthy. and straight from the farm is the best place to go. >> whether that's healthier or not, i don't know. but it makes even the -- it makes eating more interesting. >> reporter: more interesting maybe, but a new stanford university study concludes that organic foods are no more nutritious than their conventional alternatives. >> we didn't find stronger evidence of higher nutritional content in organic foods. however, we did find differences in the risk of detecting pesticide residues. >> reporter: according to the report, organic produce is 30% less likely to carry pesticide residues than other fruits and vegetables. and organic chicken and pork are 67% less likely to have bacteria resistance to common antibiot antibiotics.

it may take years to link pesticides and antibiotics to long term health problems, but these are issues we have to consider today. >> i really think people should be thinking about knowing where their food comes from, how it's grown, that it is economically, that it is environmentally sound. >> reporter: according to those who study food purchasing preferences, millennials, those under age 30 are driving the trend. >> they're choosing to want to eat more pure foods. and organics is part of that decision process. >> reporter: while organic farmers and ranchers don't claim their foods are healthier, more than half of them in a recent poll believe organic is more nutritious. your best advice, buy local. the shorter the distance between farm to table the better it's going to be. and the more nutritious. brian? >> going to have people questioning a lot of things. nancy, thanks. one more note here about what we consume these days. the number of milk drinkers is on the decline in america. milk sales in our country have fallen to the lowest level in

nearly three decades. as americans shift toward bottled water and all kinds of other drinks. up next here tonight, hundreds of beautiful trees coming down so the space shuttle can roll through the streets. that's the plan in l.a., and not everybody likes it.

some other items in the news tonight, this new book about the bin ladin raid called "no easy day" has been outselling "50 shades of grey" during the advanced sales period on amazon. because of the book by a former navy s.e.a.l. and the secrets it reveals within it, today the rear admiral who heads the navy special warfare command took the extraordinary step of reminding those under his command they must never reveal what they do on the job. and we should quickly add, most never do. in los angeles, there's growing dismay tonight over what the city is doing to make way

for the arrival of the retired space shuttle "endeavor." they are cutting down 400 trees. many of them mature beautiful trees in a city that needs them. our report tonight from nbc's mike taibbi. >> reporter: they're cutting down some 400 trees, including many mature pines and magnolias reduced to stumps, so the five story high, 78-foot wide endeavor can move down the streets. some along the south l.a. route are not amused. >> you're sitting at a stoplight, that little bit of shade is gone. it is a concrete jungle. it's more like new york than los angeles. >> that's stupid. replant them, why cut them down? >> reporter: the california science center says, once the "endeavor" is in place, they'll plant twice as many trees as will have been cut down. but removing the trees on the route selected was the only option. dismantling endeavor or airlifting it were deemed impossible. so good-bye trees. the 12 mile trip from l.a.x. to

the science center next month was supposed to be a two-day parade along this route, with an overnight slumber party included. and while that still may be true, it's not all that's true. because to get it to its final resting place on the streets broad enough to accommodate it, power lines will be raised, some streetlights will be removed, and hundreds of trees will bite the dust. >> not only do we get to participate in history, we get our trees replaced two for one. so we're very happy here in the city. >> reporter: there are plenty of angelenos who think it's worth it. >> i'm really excited to see the endeavor, it's a once in a lifetime chance, i'm glad to see it happen. >> reporter: but this is california, where anything involving trees is big news. from the plight of the giant redwoods a century ago, to the old tree downed by age and weather in north hollywood this morning. >> liftoff of the space shuttle endeavor -- >> reporter: to the revelation that moving this modern national treasure to l.a. will cost some urban greenery that goes back generations. mike taibbi, nbc news, los

angeles. >> we'll keep you updated on that story as it goes on. here's another sign of the times. according to data compiled by "usa today," voice mail is fading fast. down almost 10% in a year's time. according to the internet phone company vonage, people are sick of the process, the prompts, the elaborate introductions, and wherever possible customers prefer to send a text or e-mail instead of voice mail. up next here tonight, the games inspiring a lot of people, including young americans back from the front lines.

finally tonight, back over to london we go, we last saw you from there during those fabulously successful olympic games. londoners were justifiably so proud of pulling it off so well, and now, they get to do it all over again. the paralympics are underway. 4,000 athletes from all over the world, all of them gathered there to push what is possible. our report tonight from london and nbc's stephanie gosk. >> reporter: the paralympic games opened to a packed house. the torch was relit. the queen came again, though not

by parachute this time. >> stretch your wings and fly. >> reporter: an opening ceremony as spectacular as the last one. >> the crowds will be unprecedented. these will be games to remember. >> reporter: so far they have been. millions of brits are tuning in and buying tickets. this tv promo has been everywhere. rocketing an old public enemy song into the top ten. there was a touch of controversy. an iranian medal winner wouldn't shake kate middleton's hand for religious reasons. but mostly these games have been marked by excitement. >> we enjoyed the olympics so much, we just wanted to be a part of it. >> reporter: and like the olympics, these games are about the competition. >> very amazing how they cycle with one leg and run and stuff with no legs. >> reporter: from goal vault -- >> look at the speed of that. >> reporter: -- to wheelchair basketball to sitting

volleyball. the mantra here is don't watch out of pity, watch because it's exciting and inspiring. the athletes here say, that just like the olympics, this is about showing what human beings can do, not what they can't do. american angela madson is paralyzed from the waist down. >> somebody who doesn't believe they can and doesn't try, that's a disabled person to me. >> reporter: scott winkler, a u.s. army vet was injured in iraq. >> we're no different than anyone else. >> reporter: a former u.s. army airborne has this advice. >> get up. life is too short to lay down. go get it. >> reporter: a message that everyone, regardless of ability, can embrace. stephanie gosk, nbc news, london. >> great story to end on on a tuesday night. thank you for being here with us. we're back on in prime time tonight with the big speeches of the evening, including the first lady. our coverage begins at 10:00 eastern, 7:00 pacific. i'm brian williams.

we hope to see you right back here tomorrow evening. and we hope you can hear us even better. good night from charlotte. -- captions by vitac -- www.vitac.com patrol cars and -- the very latest on that shooting that's left a chp officer in critical condition and a suspect dead. so many have been hoping and waiting for, a firefighter who went into a coma from a heart attack battling a blaze last week has opened his eyes today.